In a known etalon-type variable spectroscopy element, two optical substrates having optical coating layers provided on opposing surfaces thereof face each other, and a gap between these optical substrates can be varied by an actuator formed of a piezoelectric device (for example, see Patent Document 1).
This variable spectroscopy element is provided with sensor electrodes of an electrostatic capacitance sensor on the opposing surfaces of the two optical substrates, and the distance between the optical substrates is detected by the electrostatic capacitance sensor, allowing the gap to be controlled.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. HEI-1-94312